Coated plastic products



Reissuecl Dec. 15, 1953 Re,

UNITED STATES PATENT OFFICE COATED PLASTIC PRODUCTS Johan Bjorksten,Madison, Wis., Stuart 0. Fledler, Cleveland, Ohio, and Luther L. Yaeger,Madison, Wis., assignors to Nash-Kelvinator Corporation, Kenosha, Wis.,a corporation of Maryland No Drawing. Original No. 2,578,665, datedDecember 18, 1951, Serial No. 730,192, February 21, 1947. Applicationfor reissue December 17,

1952, Serial No. 326,615

12 Claims. (01. 260-17) Matter enclosed in heavy brackets appears in theoriginal patent but forms no part of this reissue specification; matterprinted in italics indicates the additions made by reissue.

This invention relates to articles made of polystyrene and morespecifically to such articles, covered with a surface coating whichimparts to them a greatly enhanced resistance to abrasives,

solvents and to other destructive influences; and parency. also to modesof preparing and applying such The present invention has for an objectto surface coating materials for polystyrene. overcome the disadvantagesjust mentioned, An-

Polystyrene is a widely employed construction other object is to providea novel coating for material. For example, it is being used inrepolystyrenes which forms an integral bond therefr geration equipmentand also in automotive and m with, and which imparts to polystyreneenhanced aircraft industries for structural as Well as decresistance toscratching, reduced electrostatic orative purposes. However, the utilityof polysensitivity, and greatly enhanced resistance to styrene isgreatly restricted by certain undesircleaning fluids. A further objectis a polystyrene able properties, namely: 1. Very high electroarticleprotected by such coating. A still further static charges which causeexcessive attraction object is a process of applying to the polystyrenefor dust. 2. High susceptibility to scratching. articles a protectivecoating integrally bonded (This does not bear a direct relation to thehardthereto. Further objects will become apparent as ness of thearticle, inasmuch as the optical effects the following detaileddescription proceeds. of scratching are more pronounced with poly- Byintegral bond We mean that the coating styrene than with certain othermaterials which applied to all practical purposes forms a unity actuallyhave a lower hardness, such as, for exwith the material beneath it, sothat it cannot ample, acrylates.) 3. Clouding or dissolving of I bepeeled off or loosened as a layer, for example, the styrene surface bycommonly used cleaning by scratching with a sharp instrument. fluids. FWe have now succeeded in providing acrylate Any one of the reasons issufficient to greatly coatings which adhere firmly to polystyrene,reduce the applicability of polystyrene as a mawithout disturbing itsclarity or appearance. terial for many articles where it would.otherwise Our products and procedures are based on the be desirable byvirtue of its excellent physical and discoveries: mechanical propertiesand its relatively low price. (a) that if the active solvent in whichacrylate In the past, it has been attempted to apply to 30 resins areprepared, and furnished commercially, polystyrene various kinds ofcoating for added is distilled off to a large degree, it is thenpossible surface protection and to improve its properties. to formulatesuitable coating compositions for These attempts have all beenunsuccessful. Coatdepositing acrylate coatings on polystyrene withingsof shellac, while soluble in solvents which do out etching thepolystyrene surface: not attack the polystyrene, are not sufiiciently(b) that the etching effect of active solvents tenacious to give theprotection desired. Further can be largely checked by the inclusion ofcellumore, they are soluble in alcoholic cleaning fluids. lose esters:Ethyl Cellulose coatings f th po y yrenes and (c) that by carefulbalancing of solvent comof their derivatives have also been tried, andwhile positions, it is possible to provide a combination these possess aconsiderable resistance to many 40 solvent which dissolves and depositsacrylates, yet solvents and to electrostatic influences, they are isnon-etching to styrene: not very scratch resisting, and, above all, they(d) that cellulose esters, which otherwise do fail to bond to thepolystyrene. It can be said not adhere to polystyrene, can be brought toadgenerally that those coatings ofprior art which here firmly by theaddition of even a minor perbond to the polystyrene so as not to becomedecentage of acrylates, such as from 1% to 40%. tached therefrom aresoluble only in solvents In accordance with this invention, we employwhich are also solvents for polystyrene, and which as the principalprotective ingredient, an acrylate therefore etch and cloud it, and thatcoatings of or a methacrylate polymer. prior art reasonably suitable inother regards fail For t e ke of brevity, We shall hereafter in,- toadhere to polystyrene. clude the film-forming acrylate and methacry-Attempts made in the past to coat polystyrene with acrylate ormethacrylate type polymers failed, because the solvents necessary todissolve these etched the styrene so as to destroy its trans- Among thenumerous types of acrylate employed for the purpose of the invention,the preferred type is:

Ethyl and methyl methacrylate co-polymer made by the E. I. du Pont deNemours at C0.

Somewhat less favorable film characteristics were obtained with thefollowing type of acrylate:

Ethyl methacrylate polymer made by the Guth Products Company.

The following typesalso gave a coating, but were not preferred becauseof resistance less favorable than the preferred types of acrylatesstated above:

"Butyl methacrylate polymerized to form a solid thermoplastic powdermade by the E. I. du Pont de Nemours 8: Co.

Methyl methacrylate polymer.

One acrylate, which gave the best results, was, however, furnished, bythe manufacturer, dissolved in ethyleneglycol monoethylether acetate, inwhich solvent this resin was prepared. This solvent interfered with theproper application of the coating, by etching polystyrene. This necessitated correction, which could be accomplished:

(a) by removing a large portion of this solvent by distillation;

(b) by carrying out the manufacture of a resin in a different solventless active on styrene, e. g., ethyleneglycol monomethyl ether;

( c) by compounding with a different film form'- ing body, which has atendency to repress solvent action on styrene, e. g., a cellulose ester.

This problem, and the three remedies listed, apply to any acrylate resinprepared and furnished in a solution of an active styrene solvent. Whenan injection molding type acrylate is employed, this problem does notexist; however, the viscosities of such resins are so high as topreclude spraying as the application method, unless an unusually thincoating (less than about .001") is desired. Such solutions can beapplied by dipping the object to be coated, or by brushing.

Specific embodiments of the invention are illustrated by the followingexamples:

Example 1 30% ethyl acrylate was polymerized by refluxing with ofbenzoyl peroxide in 69 ethyleneglycolmonomethylether, until a sample ondrying formed a film having 9. mar resistance at least 10% higher thanthat of polystyrene by the A. S. T. M. Procedure D 673-421 (fallingcarborundum grit). of the product thus obtained was dissolved in 80% ofa solvent consisting of methyl ethyl ketone, 25% ethanol, and diethyleneglycol mono ethyl ether.

The resultant product was brushed on to a polystyrene object, and driedin a forced draft cabinet at 63 C. The resultant coating had asubstantially enhanced mar and solvent resistance.

Example 2 25% ethyl methacrylate monomer was polymerized by refluxing inthe solvent consisting of equal parts of ethyleneglycolmonomethylether,methyl ethyl ketone, and ethanol. A pressure was maintained so as topermit maintenance of a reaction temperature of 180 C. The reaction wascontinued until a sample removed and allowed to dry to a. film, gave 9,mar resistance at least 10% higher than that of polystyrene by the A. S.T. M. Procedure D 673-42T.

The resultant product was then sprayed on to a polystyrene object anddried at 70 C. It was found to have a substantially enhanced mar andsolvent resistance.

Example 3 Percent by weight Methyl methacrylate polymer 10 The acrylatepowder was dissolved in the acetone and esters. When uniform, theremaining solvents were blended into the mixture with agitation. Apolystyrene panel was dipped into the lacquer and dried at 55 C. Aclear, tenacious coating was deposited on the plastic. This coating had'9. mar resistance substantially higher than polystyrene and was firmlybonded thereto.

The present invention provides an article of manufacture comprising apolystyrene surface having integrally bonded thereto an acrylatecoating. In a more specific aspect it provides the combination of apolystyrene surface having integrally bonded thereto a coatingcomprising an acrylate and a cellulose ester. A coating comprising to 1%of an acrylate and from 0 to 99% of a cellulose ester may be used.Suitable cellulose esters are cellulose aceto butyrate and celluloseaceto propionate.

In the formulas given, the percentage of solids is not critical, as avariation in this factor will only affect the thickness of the resultantcoating, and not its qualities.

We may employ any other cellulose ester which is capable of forming ahard tenacious film, for example, cellulose acetate, cellulose acetatepropionate, cellulose propionate, and the like. Therein a. similarconnection of cellulose acetate hydrogen phthalate is disclosed andclaimed in our co-pending application Serial No. 730,193 filed February21, 1947.

With reference to the solvent combinations stated, instead of methylethyl ketone, we may employ any other ketone, ester, toluene or nitroaliphatic substance excepting nitro methane, which has-a boiling rangebelow about C., or combinations thereof. Instead of ethyl alcohol. wecanuse nitro methane, or any other aliphatic alcohol, or lactate, havingless than 6 carbon atoms. We can also use Butyl Cellosolve" and anyother glycol ether having a comparable or higher degree of volatility,diacetone alcohol and the like.

It is possible to work into the formulations even other solvents,plasticizers, pigments, dyestuffs. perfumes and the like as well asother resins and to co-polymerize these or their components with theacrylates disclosed. The term acrylate we understand to include suchproducts, having the essential characteristics herein described inrelation to polystyrenes. When thus modifying the compositions, thebalance between polystyrene solvents and polystyrene nons'olvents mustbe maintained. This is done in the following manner: If the coatingcomposition is turbid, the percentage of ketone type solvent or ofglycol ether ester should be increased, and likewise if the bond of thecoating to the polystyrene is poor. If, on the other hand, thepolystyrene surface is etched by the coating composition, then thepercentage of these solvents just mentioned should be reduced, in favorof nitro methane, lower aliphaic alcohols, lactates andethyleneglycolmonomethyl ester, or hydrocarbon nonsolvents such asaliphatic petroleum fractions e. g., kerosene,

or of combinations of these, or other solvents having similar solventand volatility characteristics.

Suggested ranges of percentage for these groups of solvents are asfollows:

Aliphatic ketones and esters, toluene and nitro-aliphatic substancesother than nitro- ,methane having a boiling range below 120 0.,

preferred 3 to 25%; usable 1 to 35%.

Nitromethane, aliphatic alcohols and lactates having less than 6 carbonatoms, preferred 5 to the skilled chemist to establish the properbalance for the purposes of this invention, for any particular solventshe may desire to employ.

While reference has been made throughout this application topolystyrene, it is fully understood that this term includes suchco-polymers or modified products as are commercially known under thegeneric term, styrene type resins. This includes copolymers betweenstyrenes and acrylates, polymers with acrylonitrile and like materialsknown as being suitably co-polymerizable with styrene. The di-vinylbenzenes and their polymers and co-polymers are also included in thegeneric terms polystyrenes.

It is thus seen that this invention is broad in scope. The specificranges and examples have been given to illustrate only, and not torestrict the invention in any manner; The invention is to be limitedonly by the claims in which we intend to cover all novelty inherent inthe invention as broadly as possible, in view of prior art.

Having thus disclosed our invention, we claim:

1. An article of manufacture comprising a polystyrene surface, havingintegrally bonded thereto a coating comprising a substance selected fromthe group consisting of polyethyl acrylate, polyethyl methacrylate,polymerized butyl methacryldte, ethyl and methyl methacrylate co-polymerand polymethyl methacrylate, said coating being deposited from acomposition containing from 1 to 35% of a solvent selected from thegroup consisting of aliphatic ketones and esters, toluene and nitroaliphatic substances other than nitro methane, having a boiling rangebelow 120 C.; from 2 to 45% of a solvent selected from the groupconsisting of nitromethane, aliphatic althan nitromethane having aboiling range below 120 C.; 5 to 35% of a solvent selected from theclass consisting of nitromethane, aliphatic alcohols, and lactateshaving 1 to 5 carbon atoms; and to 40% of a substance selected from thegroup consisting of diacetone alcohol, glycol ethers and esters.

3. A coating composition comprising a substance selected from the groupconsisting of polyethyl acrylate, polyethyl methacrylate, polymerz'zedbutyl methacrylate, ethyl and methyl methacrylate co-polymer andpolymethyl methacrylate and a cellulose ester, dissolved in a solventcomposition comprising from 3 to of a solvent selected from the groupconsisting of aliphatic ketones and esters,toluene, and nitroaliphaticsubstances other than nitromethane having a boiling range below 120 C.;5 to of a solvent selected from the class consisting of nitromethanealiphatic alcohols, and lactates having 1 to 5 carbon atoms; and 20 to01' a substance selected from the group consisting of diacetone alcohol,glycol ethers and esters.

4. As claim 3, the cellulose ester being cellulose aceto butyrate.

5. As claim 3, the cellulose ester being cellulose aceto propionate.

6. A coating composition comprising a substance selected from the groupconsisting of polyethyl acrylate, polyethyl methacrylate, polymerz'zedbutyl methacrylate, ethyl and methyl methacrylate co-polymer andpolymethyl methacrylate, and a film forming cellulose ester, dissolvedin a solvent comprising from 1 to 35% of a solvent selected from thegroup consisting of aliphatic ketones and esters, toluene and nitroaliphatic substances other than nitro methane, having a boiling rangebelow 120 C.; from 2 to of a solvent selected from the group consistingof nitromethane, aliphatic alcohols and lactates having 1 to 5 carbonatoms; and from 14 to of a solvent selected from the group consisting ofdiacetone alcohol, glycol ethers and esters.

7. The article of claim 1, further characterized by said coatingadditionally comprising a cellulose ester.

8. The article of claim 1, further characterized by said coatingadditionally comprising cellulose acetobutyrate.

9. The article of claim 1, further characterized by said coatingadditionally comprising cellulose acetopropionate.

10. In a process for enhancing the surface properties of polystyrene byutilizing the high specific adhesivity therefor of certain, syntheticresins, which depends on applying to a polystyrene surface syntheticresinous material having superior surface properties, dissolved in asolvent which does not dissolve or attack polystyrene, the step ofapplying to a polystyrene surface the composition of claim 2,

resins, which depends on applying to a polystyrene surface syntheticresinous material hav ing superior surface properties, dissolved in asolvent whichdoes not dissolve or attack poly styrene, the step ofapplying to a polystyrene surface the composition of claim 6.

I JOHAN BJORKSTEN.

STUART O. FIEDLER. LUTHER L. YAEGER.

References Cited in the file of this patent or the original lpaten'tUNITED STATES PATENTS Number Name Date 2,071,419 1Moss Feb. 23, 19372,034,415 Strain June 22, 1937 2,238,694 Graves Apr. 15, 1941 2,254,904Moss Sept. 2, 1941 2 ,292,393 Mitchell Aug. 11, 1942 2,332,461 Muskat eta1 M Oct. 19, 1943

